(A) Field of the Invention
The present invention relates to an optically modulated scatterer and array thereof, and more particularly, to an optically modulated scatterer and array thereof for measuring a spatial distribution of an electromagnetic signal without interference. The optically modulated scatterer and array thereof is an important tool for measuring the spatial distribution of the electromagnetic field.
(B) Description of the Related Art
Since a wireless communication system uses an antenna to transmit and receive an electromagnetic signal, how to make the electromagnetic field emitted by the antenna to comply with the specifications is an important subject for improving the antenna quality. In addition, the intensity of the electromagnetic wave emitted by the wireless communication product must be lower than the specific absorption rate (SAR) specified by the international safety standard to come into the market, therefore the SAR measurement technique is very important for the development of the cell phone. Presently, there are many electromagnetic wave measurement techniques; one of them utilizes the modulated scatterer to measure the distribution of the electromagnetic field.
The conventional technique uses a modulated scatterer array to measure the electromagnetic field, wherein an electrical modulating signal is transmitted by a conductive wire to modulate a diode inside the scatterer and incorporates fast scanning to measure the electromagnetic field. The bias voltage applied to the diode inside the scatterer is transmitted through the conductive wire; however, the conductive wire will irradiate electromagnetic waves, which interfere with the electromagnetic signal to be measured. U.S. Pat. No. 4,305,153 discloses an electromagnetic field measurement technique using a light beam incorporating a chopper to modulate the diode inside the scatterer, wherein the bias voltage is supplied by a solar cell. In addition, G. Hygate et al. disclose an electromagnetic field measurement technique without electrical interference, which uses a phototransistor to produce an optically modulated scatterer, i.e., uses optical device rather than the conductive wire to modulate the scatter (SEE: Measuring microwave fields directly with an optically modulated scatterer, 1990, Meas. Sci. Technol., and A Probe for Making Near-Field Measurements with Minimal Disturbance: The Optically Modulated Scatterer). However, G. Hygate et al. only disclose the utilization of the optically modulated scatterer in the electromagnetic signal sensing system, the detailed structure of the optically modulated scatterer is not disclosed. Under this situation, it is difficult for one skilled in the art to overcome the shortcomings of the prior art using the disclosure by G. Hygate et al.